In recent years, significant advancements have been made in reduction of size and weight in electronic apparatuses. This trend of size reduction and weight reduction is particularly remarkable in portable apparatuses such as cellular phones. In relation to this, there is a demand for size reduction of printed circuit boards carrying various electronic components such as semiconductor devices and passive components.
In relation to the foregoing trend of technology, there is a demand for a built-in charging control circuit used with portable devices for controlling charging of secondary battery pack, such that the charging control circuit is integrated into the secondary battery pack. Thus, especially severe demand of size reduction is imposed on such a charging control circuit of secondary battery pack.
Meanwhile, electrical connection between the electrode of a secondary battery and a charging control circuit is achieved usually by using an interconnection lead of a nickel plate in the case the secondary battery is accommodated in the battery pack, in view of the fact that a nickel plate is used for the interconnection pattern taking out the electric power from the electrode with the secondary battery accommodated in a battery pack. By using such a nickel plate for the interconnection pattern, it becomes possible to connect the interconnection pattern to the electrode simply and directly by way of spot welding. Further, by using such a nickel plate, it becomes possible to eliminate the need of providing additional interconnection patterns for electrical interconnection between the secondary battery and the charging control circuit. Thereby, the size of the charging control circuit can be reduced further.
On the other hand, the use of such a nickel plate for the interconnection between the secondary battery and the charging control circuit imposes a demand to such a battery pack in that the external terminal of the printed circuit board carrying the charging control circuit should allow spot welding of nickel plate.
In order to meet for this demand, the external interconnection terminal of the printed circuit board used with such a secondary battery pack has been formed by forming a land on the surface of a base substrate of the printed circuit board in the form of a metal foil and by soldering a nickel plate on such a land.
For example, there is an external interconnection terminal as set forth in Patent Reference 1 in which a nickel plate is soldered upon a land formed on the surface of a printed circuit board via solder resist patterns formed so as to divide the land surface evenly. With such a construction, the tensile force acting upon the nickel plate with melting of solder is cancelled out by the tensile forces caused in the respective divided portions of the land. Thereby, precision of alignment of the nickel plate on the printed circuit board is improved together with the mechanical strength.
Further, there is proposed another construction as set forth in Patent Reference 2, in which a nickel plate having a U-shaped cutout or hole is soldered upon the surface of a printed circuit board. With such a construction, total length of solder filet formed at the time of soldering is increased, and mechanical strength of contact is improved at the same time.
Further, Patent Reference 3 discloses a construction of interconnection terminal formed on a printed circuit board, in which a metal plate is soldered upon a land formed on the printed circuit board for external connection, wherein a solder resist layer is formed between the land and the part of the metal plate on which an external lead wire is to be soldered. With such a construction, melting of the solder provided between the metal plate and the land is avoided at the time of soldering a lead wire to the metal plate, and drifting of the metal plate away from the land is prevented.
Thus, with this reference, the lead wire is soldered on the foregoing part of the metal plate in which the solder resist exists between the metal plate and the land. By soldering the lead wire to such a part of the metal plate not soldered directly to the land, it becomes possible to prevent the melting of the solder layer connecting the metal plate to the land. Thereby, the problem of displacement of the metal plate with regard to the land during the soldering work of the lead wire as a result of melting of the solder between the is successfully prevented.